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MathNet 2020 — Math Olympiad Vault — Part 04 Question 106

Math Olympiad Vault · MathNet 2020 — Math Olympiad Vault — Part 04

Question 106

(a) Suppose $n=k^2$ is a perfect square. Prove that the number of positive divisors of $n$ below $k$ equals the number above $k$.
(b) Prove that $k^2$ has at most $2k-1$ positive divisors.
(c) Find every positive integer $k$ for which $k^2$ has exactly $2k-1$ positive divisors.